In many areas of technology, e.g., in refrigeration technology, the individual leaks expected in the system during operation must be localized and quantified, if necessary, and the total leak rate of the system must also be determined.
Methods for determining a total leak rate based on a pressure drop or pressure increase test are known. The system to be tested is filled up to the setpoint pressure and is checked for a change in pressure after a time period.
However, the known pressure drop tests for determining the total leak rate are subject to substantial inaccuracies. First, these tests are based on the pressure measurement technology used, which generally allows a resolution of only 10,000 Pa. Even in the case of small internal system volumes, the testing required, taking into account the maximum allowed leak rates, would take several days, depending on the test pressure, because only then would it be possible to determine whether there has actually been a change in pressure. Such long measurement times have the disadvantage that temperature changes not taken into account will greatly distort the measuring results. In the case of large internal volumes of several dm3 and only small total leak rates, such a measurement is no longer feasible at all.
However, even an increase in resolution to 5 Pa, for example, would still require a measurement time of several minutes. Even with such short measurement times, however, changes in temperature in the system to be tested occur, resulting in inaccuracies in the measuring result.
Another disadvantage of the known pressure drop test is that the internal volume of the system is not known at all or not known with sufficient accuracy. However, since the volume of the system has a linear influence on the leak rate, this results in further inaccuracies in the measured result. At the same time, wrong conclusions are drawn with regard to the test time required and thus another source of error is introduced because of this lack of information. Additional error sources arise from relationships between leak rates in testing and during operation, about which and about the way they depend on changes in pressure, temperature, and viscosity little is known in general; also, there is the failure to take into account the leak rate of the measuring system itself. On the whole, the known methods for determining the total leak rate of a system only constitute an approximate leakage test.
Determination of the total leak rate of a system, e.g., a pressure device or a group of pressure devices, may also be estimated by multiplying all potential leakage sites, such as solders, joints, screw connections, etc., by the proven leak rate of the leakage sites. However, the problem then arises that if the leak rate of a potential leakage site is not detectable, the calculation will yield a negligible total leak rate, although in fact there is a relevant leak rate which may be far greater than that maximally allowed.
In addition, the total leak rate of the system is also derived by determining the quantity of process medium such as refrigerant to be resupplied during the course of operation. However, when a system is already in operation, repairing a leak is cost-intensive and time-consuming and in particular does not yield the desired accurate results.
Therefore, it would be desirable to provide a method with which small total leak rates may be determined with a high accuracy within a suitable time period, even in systems having large volumes of several dm3.